<template>
  <div class="pagination">
    <button :disabled="pageNo==1" @click="$emit('getPageNo',pageNo-1)">←上一页</button>
    <button v-if="startAndEnd.start>1"
            @click="$emit('getPageNo',1)"
            :class="{active:pageNo==1}"
    >1</button>
    <button v-if="startAndEnd.start>2">...</button>

    <button v-for="(page,index) in startAndEnd.end" :key="index"
            v-if="page>=startAndEnd.start"
            :class="{active:pageNo==page}"
    >{{page}}
    </button>

    <button v-if="startAndEnd.end<totalPage-1">...</button>
    <button v-if="startAndEnd.end<totalPage"
            :class="{active:pageNo==totalPage}"
    >{{totalPage}}</button>
    <button
            :disabled="pageNo==totalPage"
            @click="$emit('getPageNo',pageNo+1)"
    >下一页»</button>

    <button style="margin-left: 30px">共{{total}}条</button>
    </div>
</template>

<script>
export default {
  name: "Pagination",
  props: ["total", "pageSize", "pageNo", "continues"],
  computed: {
    //分页器一共多少页【总条数/每页展示条数】
    totalPage() {
      //向上取整数
      return Math.ceil(this.total / this.pageSize);
    },
    //底下的代码是整个分页器最重要的地方[算出连续五个数字、开头、结尾]
    startAndEnd() {
      //算出连续页码:开始与结束这两个数字
      let start = 0, end = 0;
      const { totalPage, continues, pageNo } = this;
      //特殊情况:总共页数小于连续页码数
      if (totalPage < continues) {
        start = 1;
        end = totalPage;
      } else {
        //正常情况：分页器总页数大于连续页码数
        start = pageNo - parseInt(continues / 2);
        end = pageNo + parseInt(continues / 2);
        //约束start|end在合理范围之内
        //约束头部
        if (start < 1) {
          start = 1;
          end = continues;
        }
        //约束尾部
        if (end > totalPage) {
          end = totalPage;
          start = totalPage - continues + 1;
        }
      }
      return { start, end };
    },
  },
};
</script>

<style lang="less" scoped>
  .pagination {
    button {
      margin: 0 5px;
      background-color: #f4f4f5;
      color: #606266;
      outline: none;
      border-radius: 2px;
      padding: 0 4px;
      vertical-align: top;
      display: inline-block;
      font-size: 13px;
      min-width: 35.5px;
      height: 28px;
      line-height: 28px;
      cursor: pointer;
      box-sizing: border-box;
      text-align: center;
      border: 0;

      &[disabled] {
        color: #c0c4cc;
        cursor: not-allowed;
      }

      &.active {
        cursor: not-allowed;
        background-color: #99cafc;
        color: #fff;
      }
    }
  }
</style>
